The natural multisystemic disease syndromes of inbred and crossbred New Zealand mice are well recognized laboratory animal models of human diseases of unknown etiology: systemic lupus erythematosus, autoimmune hemolytic anemia, and lymphoma/leukemia. As we have shown, the natural history of the murine disease is related to the expression of a murine endogenous oncornavirus C (type C RNA tumor virus) and to pathogenetic antibody responses both to self antigens and to endogenous viral protein antigens. The overall objective of this project is to elucidate the genetic, viral, and immunological determinanats of disease in the animal models and to apply the knowledge gained to the study of the cause and nature of corresponding human diseases. Pursuing this line of research, we have recently found and located microscopically a mammalian oncornavirus-related protein antigen in pathological specimens of human tissues in the disease, systemic lupus erythematosus. The further characterization of the nature and significance of this antigen is under study. BIBLIOGRAPHIC REFERENCES: An antigen related to mammalian type-C RNA viral p30 proteins is located in the renal glomeruli in human systemic lupus erythematosus. Mellors, R.C., and Mellors, J.W. Proc. Natl. Acad. Sci. USA, in press, 1976. Electron microscopic study of distinctive structures in peripheral blood lymphocytes obtained from twins with systemic lupus erythematosus. Imamura, M., Block, S.R., and Mellors, R.C. Am. J. Path., in press, 1976.